Contrasting impact of different Mediterranean cyclones on the hydrological cycle and ocean heat content

Abstract. Mediterranean cyclones (MCs) play a crucial role in the Mediterranean hydrological cycle (MHC), driving up to 70 % of precipitation and 50 % of evaporation totals, and larger fractions of their extremes. Therefore, regional sensitivity to warming is often associated with long-term changes of MCs. These may lead to regional climate feedback through pathways linked directly or indirectly to the MHC: from decreasing cloud cover and precipitation to increased water-vapor uptake. However, the ability of MCs to generate coherent climate feedback is under ongoing debate. Moreover, given the large diversity of processes driving MCs, the role of each in the MHC and their variability remains unexplored. Our recent process-based MC classification allows the breakdown of MC’s contribution to the MHC under different dominant cyclogenetic processes. Based on 1-hourly ECMWF ERA5 reanalysis data (1979–2020), 3190 MC tracks are analyzed. We first quantify the total contribution of MCs to the MHC following the cyclone tracks. We analyze the spatial and temporal patterns of the annually accumulated cyclone-induced precipitation (P) and surface evaporation (E). The process-based classification allows the quantification of independent contributions from various cyclone drivers to cyclone-induced P and E and their long-term trends. The results show that the overall annual P-E residual associated with MCs is positive but decreases over time, losing ~0.5 mm/yr per year. The classification reveals opposing roles and long-term trends in the annual contributions of each cyclone driver, shifting the balance between cyclone-induced P and E from P-dominated towards E-dominated MCs. These changes are primarily due to reduced precipitation associated with double-jet MCs and daughter cyclones and increased evaporation associated with thermal lows (−0.2 mm/year, each), alternately driven by changes in frequency and/or flux intensities of specific cyclone drivers. Mainly, a sharp rise in frequency affects heat lows, while double-jet cyclones are mostly affected by decreasing precipitation rates. The downward impact of MCs on the Mediterranean Sea heat content also varies sharply between MC types: while MCs generally draw heat from the Mediterranean, certain MC types have the opposing effect, adding further heat. Beyond providing a framework for follow-up analysis of MC impact on the MHC in future climate simulations, the results highlight the independent and opposing contributions of different MC drivers to the Mediterranean heat content, enhancing our understanding of their dynamic response to warming and its impact on society.